AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Origin and Thermal Maturity of Cretaceous Shales from the Orange Basin: Insights from Inorganic Geochemistry
(1) Obafemi Awolowo University, Ile-Ife, Nigeria.
Trace elements in kerogen fraction of shale samples from two wells obtained from the Cretaceous units of the Orange Basin, South Africa were determined using x-ray fluorescence spectrometric method, in order to determine their distribution and geochemical significances. The concentrations of the elements (As, Ce, Co, Cu, Fe, Mo, Ni, Pb, V and Zr) determined ranged from 0.64 - 47300 ppm for the samples analysed.
The total organic carbon (TOC) values indicate that the samples are organic rich but did not show any trend with the distribution of the trace metals except Ce, Mo, and Pb. Dendrogram cluster analysis discriminated the samples into three groups on the basis of level of their thermal maturity. Thermal maturity has significant effect on the distribution of the trace metals. Co/Ni and V/Ni ratios and cross plot of the absolute values of vanadium and nickel indicate that the samples had strong marine organic matter input. The vanadium and nickel contents and V/(V+Ni) ratio indicate that the organic matter of the source rocks were deposited in reducing conditions. Despite the similarities in the organic matters source input and depositional environment of the organic matter of the samples from the two well, cross plots of Co/Ni versus V/Ni and Mo/Ni versus Co/Ni were able to reveal their subtle differences. Cluster analysis of the samples was able to reveal the subtle thermal maturity differences of the samples.